Ion liquid composition for carbon dioxide separation membrane, carbon dioxide separation membrane holding the same, and carbon dioxide concentration device provided with the carbon dioxide separation membrane

Abstract

Provided is an ionic liquid composition for a carbon dioxide separation membrane that can be used for the separation of carbon dioxide from a high partial pressure to a low partial pressure, particularly 1 kPa or less, and a carbon dioxide separation membrane that holds the composition, and a carbon dioxide concentration device provided with the carbon dioxide separation membrane, in which the ionic liquid composition is formed by combining an ionic liquid (I) in which an ammonium having one or more primary or secondary amino groups in the cation, and an ethylenediamine or propylenediamine skeleton, and an ionic liquid (II) in which the cation does not have a primary or secondary amino group, and the anion is an oxoacid anion, and in which the permeability and selectivity of CO2 of the carbon dioxide separation membrane can be improved, and carbon dioxide from a high partial pressure to a low partial pressure of 1 kPa or less can be selectively separated and recovered.

Description

Technical Field

[0001] The present invention relates to an ionic liquid composition for a carbon dioxide separation membrane, a carbon dioxide separation membrane having the composition, and a carbon dioxide concentration apparatus having the carbon dioxide separation membrane. Background Technology

[0002] Technology for separating and recovering carbon dioxide is needed for the production of hydrogen and methane using natural gas as raw materials, and for maintaining enclosed living environments such as outer space and the ocean. In addition, from the perspective of reducing greenhouse gas emissions, research should be actively conducted on large emission sources such as thermal power plants and iron smelters, as well as carbon dioxide fertilization in the agricultural sector.

[0003] Representative carbon dioxide gas separation technologies include: (1) chemical absorption, which selectively absorbs carbon dioxide from a mixed gas containing carbon dioxide into a solvent through a chemical reaction, and then recovers carbon dioxide by releasing it from the solvent through a reverse reaction; (2) physical absorption, which selectively absorbs carbon dioxide from a mixed gas containing carbon dioxide without a chemical reaction, and recovers carbon dioxide by releasing it from the solvent through depressurization; and (3) membrane separation, which utilizes the partial pressure difference of carbon dioxide before and after the membrane to supply the target gas containing carbon dioxide from one side of the membrane, and selectively transports and separates the carbon dioxide in the target gas to the other side of the membrane, etc.

[0004] Ionic liquids are typically composed of only cations and anions and are liquid salts that have melting points near or below room temperature. Characteristics of ionic liquids include: being liquid over a wide temperature range, having very low vapor pressure (non-volatile), flame retardancy, excellent heat resistance, chemical stability, a wide potential window, high ionic conductivity, and the ability to dissolve a wide variety of chemical species.

[0005] Therefore, ionic liquids have been studied extensively as functional materials such as electrolytes in electrochemical devices, solvents, actuators, and lubricants in various processes such as separation and purification, and organic reactions.

[0006] In carbon dioxide separation and recovery technologies, ionic liquids also possess these characteristics, especially the non-volatile and low specific heat properties required for carbon dioxide absorbents. Therefore, they are being studied for use as absorbents for carbon dioxide.

[0007] For example, it has been proposed to use chemical absorption ionic liquids, such as ionic liquids containing amino groups in cations, as absorbents in chemical absorption methods (Patent Documents 1, 2, 3), and to use ionic liquids as solvents in non-aqueous absorbents containing amine compounds (Patent Document 4, Non-Patent Document 1), etc.

[0008] Furthermore, it has been proposed that, in physical absorption methods, ionic liquids with excellent physical absorption properties, such as ionic liquids that use imidazolium-based cations without amino groups, be used as absorbents (Patent Documents 5-8).

[0009] On the other hand, membrane separation utilizes the difference in solubility and diffusivity within the membrane to separate gases. Therefore, to improve the separation efficiency of carbon dioxide, it is necessary to increase both the permeability and selectivity of carbon dioxide. However, it is known that in polymer membranes used as conventional carbon dioxide separation membranes, increasing the selectivity reduces the permeability, and there is a limit to the improvement of the permeability and selectivity of carbon dioxide using polymer membranes.

[0010] To exceed this limit, it is effective to use a substance called a carrier, which is transported by selectively and reversibly chemically reacting with specific components in the target gas.

[0011] When using a liquid membrane containing the aforementioned carrier as a carbon dioxide separation membrane, selective transport based on the chemical reaction between carbon dioxide and the carrier allows for high selectivity separation of carbon dioxide compared to conventional polymer membranes, and the permeation rate of carbon dioxide through the membrane is also faster. However, when using membranes with volatile, conventional solvents, the gas separation function of the membrane is deactivated due to solvent evaporation, thus limiting its long-term usability.

[0012] Therefore, it was proposed to use a liquid film containing a non-volatile ionic liquid as the carrier, instead of a volatile solvent.

[0013] For example, a liquid membrane containing an ionic liquid having an amino group in the cation has been proposed. In the aforementioned Patent Document 1, it is described that a porous liquid membrane formed by impregnating an absorbent having an ionic liquid having a primary amino group in the cation as the main component is used as a carbon dioxide separation membrane.

[0014] Furthermore, in Patent Document 9, an ionic liquid composed of an amino-containing cation such as 1-(3-aminopropyl)-3-methylimidazolium is used in a liquid membrane in which an ionic liquid is held in the pores of a porous membrane for the purpose of separating and recovering carbon dioxide.

[0015] In addition, carbon dioxide separation membranes using ionic liquids with imidazolium cations, such as 1,3-dialkylimidazolium, have been proposed (Patent Documents 10 and 11, Non-Patent Documents 2 and 3).

[0016] Furthermore, Patent Document 12 proposes a carbon dioxide separation membrane suitable for carbon dioxide fertilization in the agricultural field, comprising an ionic liquid affinity porous layer that holds a liquid containing an ionic liquid within pores. In this document, examples of ionic liquids used in this separation membrane include ionic liquids containing cations selected from ammonium, imidazolium, and phosphonium groups, and anions selected from fluoride-containing anions, cyanide-containing anions, and anions derived from amino acids. Preferably, [P...] 4444 Chemical formula [R3R'P] (e.g., Pro) + An ionic liquid composed of phosphonium (where R is an alkyl group with 2 to 6 carbon atoms and R' is an alkyl group with 4 to 16 carbon atoms) and anion derived from proline.

[0017] Existing technical documents

[0018] Patent documents

[0019] Patent Document 1: Japanese Patent Application Publication No. 2006-36950

[0020] Patent Document 2: Japanese Patent Application Publication No. 2012-55785

[0021] Patent Document 3: Japanese Patent Application Publication No. 2016-10760

[0022] Patent Document 4: Japanese Patent Application Publication No. 2017-104775

[0023] Patent Document 5: Japanese Patent Application Publication No. 2006-305544

[0024] Patent Document 6: Japanese Patent Application Publication No. 2009-106909

[0025] Patent Document 7: Japanese Patent Publication No. 2011-510811

[0026] Patent Document 8: Japanese Patent Application Publication No. 2016-77935

[0027] Patent Document 9: U.S. Patent Publication No. 2014 / 0283839

[0028] Patent Document 10: Japanese Patent Application Publication No. 2010-214324

[0029] Patent Document 11: International Publication No. 2013 / 118776

[0030] Patent Document 12: International Publication No. 2018 / 211945

[0031] Non-patent literature

[0032] Non-Patent Literature 1: Mitsuo Kankubo et al., "The Solvent Effect of Amine Compounds in Non-Aqueous Solvents on CO2 Absorption," 40th Symposium on Solution Chemistry, October 18, 2017

[0033] Non-patent literature 2: Takashi Makino, et al. International Journal of Membrane Science and Technology, 2015, 2, 14-20

[0034] Non-patent literature 3: Kenta Fuji, et al., Chemistry Letters, 2015, 44, 17-19 Summary of the Invention

[0035] The problem the invention aims to solve

[0036] To effectively utilize unused carbon dioxide as a carbon source, technologies for efficiently separating and recovering carbon dioxide are needed. Previous developments primarily focused on separating and recovering high-concentration (high partial pressure) carbon dioxide, but in recent years, there has also been a need to develop technologies for separating and recovering low-concentration (low partial pressure) carbon dioxide, assuming it originates from multiple sources.

[0037] Therefore, as one of the promising separation and recovery technologies, it is expected that the above-mentioned high carbon dioxide permeation selectivity membrane separation method using a carrier may be able to achieve this.

[0038] For example, Patent Document 11 discloses a carbon dioxide permeable membrane having an amino acid ionic liquid and a porous membrane impregnated with the amino acid ionic liquid, wherein the amino acid liquid contains 3 to 50% by mass water, which maintains high carbon dioxide permeability and carbon dioxide / nitrogen selectivity even at low carbon dioxide partial pressures. It also describes that the carbon dioxide partial pressure in the mixed gas can be 15 kPa. Furthermore, specifically, a diagram illustrates the use of [P] having anions derived from glycine. 4444 [Gly] or [emim] [Gly], the result is measured while varying the partial pressure within the range of 2 kPa to 30 kPa.

[0039] However, no carbon dioxide separation membrane has yet been found that can efficiently separate carbon dioxide at low partial pressures down to below 1 kPa.

[0040] The present invention was made in view of the current situation, and its technical problem is to provide an ionic liquid composition for a carbon dioxide separation membrane that can be used to separate carbon dioxide from high partial pressure to low partial pressure, especially below 1 kPa, a carbon dioxide separation membrane that holds the composition in the pores, and a carbon dioxide concentration apparatus having the carbon dioxide separation membrane.

[0041] Technical solution

[0042] In order to efficiently separate and recover carbon dioxide from the atmosphere using liquid membranes containing ionic liquids, it is necessary to improve the permeability of carbon dioxide under low carbon dioxide partial pressure conditions and increase the selectivity of carbon dioxide (CO2) relative to nitrogen (N2) (hereinafter referred to as "CO2 selectivity").

[0043] In membrane separation, gas permeability is expressed as the product of gas solubility and gas diffusion rate. To improve CO2 permeability and CO2 selectivity in a membrane solution containing an ionic liquid as a carrier, it is important to increase the solubility of carbon dioxide relative to the ionic liquid as a carrier and suppress the solubility of nitrogen, thereby increasing the diffusion rate of the carrier that has chemically reacted with carbon dioxide.

[0044] Therefore, the inventors tried the ionic liquid described in Patent Document 3, which uses ammonium having one or more primary or secondary amino groups and an ethylenediamine or propylenediamine skeleton as an ionic liquid with excellent chemical absorption properties, and the ionic liquid described in the document used as a diluent, but found that it was impossible to improve the permeability selectivity of carbon dioxide (see Comparative Examples 1 to 8 described below).

[0045] Therefore, further repeated studies have shown that by using an ionic liquid composition consisting of an ionic liquid (I) having one or more primary or secondary amino groups in the cation and an ammonium skeleton of ethylenediamine or propylenediamine, and an ionic liquid (II) having no primary or secondary amino groups in the cation and an oxyacid anion, the CO2 permeability and CO2 selectivity of the carbon dioxide separation membrane can be improved. Furthermore, it has been found that even carbon dioxide with low partial pressure can be selectively separated and recovered.

[0046] This invention is based on the above insights. In order to solve the above technical problems, the following methods are adopted in this invention.

[0047] [1] An ionic liquid composition for a carbon dioxide separation membrane, characterized in that it is used in a carbon dioxide separation membrane,

[0048] The ionic liquid composition for the carbon dioxide separation membrane contains ionic liquid (I) and ionic liquid (II).

[0049] The cation of the ionic liquid (I) is an ammonium having one or more primary or secondary amino groups and an ethylenediamine or propylenediamine skeleton.

[0050] The cation of the ionic liquid (II) does not have a primary or secondary amino group, and the anion is an oxyacid anion.

[0051] [2] The ionic liquid composition for carbon dioxide separation membrane according to [1], wherein the ammonium is selected from one or more of 2-aminoethylammonium, 2-(N-hydroxyethylamino)ethylammonium, 3-aminopropylammonium, 3-(N-methylamino)propylammonium, 2-(2-(aminoethyl)amino)ethylammonium and 2-(2-(2-(aminoethyl)aminoethyl)amino)ethylammonium).

[0052] [3] The ionic liquid composition for carbon dioxide separation membrane according to [1] or [2], wherein the anion of the ionic liquid (I) is bis(trifluoromethylsulfonyl)amide.

[0053] [4] An ionic liquid composition for carbon dioxide separation membrane according to any one of [1] to [3], wherein the oxyacid anion is selected from one or more of carboxylates, phosphates and phosphonates.

[0054] [5] The ionic liquid composition for carbon dioxide separation membrane according to [4], wherein the oxyacid anion is selected from one or more of acetate, 2-(1-methoxyethoxy)propionate and methylphosphonate.

[0055] [6] The ionic liquid composition for carbon dioxide separation membrane according to [4] or [5], wherein the cation of the ionic liquid (II) is one or more selected from 1-ethyl-3-methylimidazolium, N,N-diethyl-N-methyl-N-heptylammonium and N,N-diethyl-N-methyl-N-(6-hydroxyhexyl)ammonium.

[0056] [7] A carbon dioxide separation membrane, characterized in that it contains the ionic liquid composition for carbon dioxide separation membrane as described in any one of [1] to [6].

[0057] [8] The carbon dioxide separation membrane according to [7] is characterized in that the carbon dioxide separation membrane comprises an ionic liquid affinity porous layer and an ionic liquid non-affinity porous layer, wherein the ionic liquid affinity porous layer retains the ionic liquid composition for the carbon dioxide separation membrane in the pores.

[0058] [9] The carbon dioxide separation membrane according to [8], wherein the ionic liquid affinity porous layer comprises an inorganic material.

[0059]

[10] The carbon dioxide separation membrane according to [9], wherein the inorganic material comprises metal oxide particles with an average particle size of 0.001µm to 5µm based on the number of particles.

[0060]

[11] The carbon dioxide separation membrane according to any one of [8] to

[10] , wherein the average thickness of the ionic liquid affinity porous layer is 0.01µm to 10µm.

[0061]

[12] A carbon dioxide separation membrane according to any one of [7] to

[11] , wherein the carbon dioxide separation membrane is used to separate and concentrate carbon dioxide with a partial pressure of less than 1 kPa.

[0062]

[13] A carbon dioxide concentration apparatus comprising any one of [7] to

[12] carbon dioxide separation membrane.

[0063] Invention Effects

[0064] The ionic liquid composition for carbon dioxide separation membranes according to the present invention can improve CO2 permeability and CO2 selectivity, and can efficiently separate and recover carbon dioxide from high partial pressure to low partial pressure below 1 kPa. Attached Figure Description

[0065] Figure 1 This is a schematic diagram illustrating the apparatus used to measure the CO2 and N2 permeability of a CO2 separation membrane.

[0066] Figure 2 This is a graph showing the partial pressure dependence of the CO2 permeation coefficient of the CO2 separation membrane (Comparative Example 1) using [emim][DCA].

[0067] Figure 3 This is a graph showing the partial pressure dependence of the N2 permeation coefficient of the CO2 separation membrane (Comparative Example 1) using [emim][DCA].

[0068] Figure 4 This is a graph showing the partial pressure dependence of CO2 selectivity of the CO2 separation membrane (Comparative Example 1) using [emim][DCA].

[0069] Figure 5 This is a graph showing the partial pressure dependence of the CO2 permeation coefficient of the [emim][Tf2N] system CO2 separation membranes (Comparative Examples 2-8).

[0070] Figure 6 This is a graph showing the partial pressure dependence of the N2 permeation coefficient of CO2 separation membranes (Comparative Examples 2-8) based on the [emim][Tf2N] system.

[0071] Figure 7This is a graph showing the partial pressure dependence of CO2 selectivity of CO2 separation membranes (Comparative Examples 2-8) based on the [emim][Tf2N] system.

[0072] Figure 8 This is a graph showing the temperature dependence of the CO2 permeation coefficient of the [emim][Tf2N] system CO2 separation membranes (Comparative Examples 2 and 5).

[0073] Figure 9 This is a graph showing the temperature dependence of the N2 permeation coefficient of the CO2 separation membranes (Comparative Examples 2 and 5) based on the [emim][Tf2N] system.

[0074] Figure 10 This is a graph showing the temperature dependence of CO2 selectivity of the [emim][Tf2N] system CO2 separation membranes (Comparative Examples 2 and 5).

[0075] Figure 11 This is a graph showing the compositional dependence of the CO2 permeation coefficient of CO2 separation membranes of the [emim][MeHPO3] system (Examples 1-6, Comparative Examples 8 and 9).

[0076] Figure 12 This is a graph showing the composition dependence of the N2 permeation coefficient of CO2 separation membranes (Examples 1-6, Comparative Examples 8 and 9) based on the [emim][MeHPO3] system.

[0077] Figure 13 This is a graph showing the composition dependence of CO2 selectivity of CO2 separation membranes of the [emim][MeHPO3] system (Examples 1-6, Comparative Examples 8 and 9).

[0078] Figure 14 This is a graph showing the CO2 partial pressure dependence of the CO2 permeation coefficient of CO2 separation membranes of the [emim][MeHPO3] system (Examples 1-6, Comparative Examples 8 and 9).

[0079] Figure 15 This is a graph showing the dependence of the N2 permeation coefficient on the CO2 partial pressure of CO2 separation membranes of the [emim][MeHPO3] system (Examples 1-6, Comparative Examples 8 and 9).

[0080] Figure 16 This is a graph showing the CO2 partial pressure dependence of CO2 selectivity for CO2 separation membranes of the [emim][MeHPO3] system (Examples 1-6, Comparative Examples 8 and 9).

[0081] Figure 17This is a graph showing the composition dependence of CO2 selectivity and N2 permeation coefficient for CO2 separation membranes of the [emim][AcO] system and the [emim][1O2OPrO] system (Examples 7-11, Example 15, Comparative Examples 8, 10, 11).

[0082] Figure 18 This is a graph showing the composition dependence of CO2 selectivity of CO2 separation membranes of the [emim][AcO] system and the [emim][1O2OPrO] system (Examples 7-11, Example 15, Comparative Examples 8, 10, 11).

[0083] Figure 19 This is a graph showing the CO2 partial pressure dependence of the CO2 permeation coefficient of the [emim][AcO] system CO2 separation membranes (Examples 8, 12, 13, and Comparative Example 10).

[0084] Figure 20 This is a graph showing the dependence of the N2 permeation coefficient on the CO2 partial pressure of CO2 separation membranes (Examples 8, 12, 13, and Comparative Example 10) based on the [emim][AcO] system.

[0085] Figure 21 This is a graph showing the CO2 partial pressure dependence of CO2 selectivity for CO2 separation membranes of the [emim][AcO] system (Examples 8, 12, 13, and Comparative Example 10).

[0086] Figure 22 This is a graph showing the composition dependence of the CO2 permeation coefficient of CO2 separation membranes of the [emim][AcO] system (amine variation) (Examples 8, 14, 16-20, Comparative Examples 8, 10, 12).

[0087] Figure 23 This is a graph showing the composition dependence of the N2 permeation coefficient of CO2 separation membranes (Examples 8, 14, 16-20, Comparative Examples 8, 10, 12) of the [emim][AcO] system (amine variation).

[0088] Figure 24 This is a graph showing the composition dependence of CO2 selectivity of CO2 separation membranes of the [emim][AcO] system (amine variation) (Examples 8, 14, 16-20, Comparative Examples 8, 10, 12).

[0089] Figure 25 It means [N] 1227 [AcO] series and [N] 1226OH Composition dependence of CO2 permeation coefficient of AcO-based CO2 separation membranes (Examples 21, 22, Comparative Examples 8, 13, 14).

[0090] Figure 26 It means [N]1227 [AcO] series and [N] 1226OH Compositional dependence of N2 permeation coefficient of [AcO]-based CO2 separation membranes (Examples 21, 22, Comparative Examples 8, 13, 14).

[0091] Figure 27 It means [N] 1227 [AcO] series and [N] 1226OH Compositional dependence of CO2 selectivity of AcO-based CO2 separation membranes (Examples 21, 22, Comparative Examples 8, 13, 14) Detailed Implementation

[0092] The present invention is characterized by the use of an ionic liquid composition for carbon dioxide separation membranes. As an ionic liquid composition for carbon dioxide separation membranes, the ionic liquid composition for carbon dioxide separation membranes contains an ionic liquid (I) and an ionic liquid (II). The cation of the ionic liquid (I) is an ammonium having one or more primary or secondary amino groups and an ethylenediamine or propylenediamine skeleton. The cation of the ionic liquid (II) does not have a primary or secondary amino group, and the anion is an oxyacid anion.

[0093] The following describes in detail the ionic liquid composition for carbon dioxide separation membrane of the present invention, the carbon dioxide separation membrane holding the composition, and the carbon dioxide concentration apparatus having the carbon dioxide separation membrane. However, these descriptions are for the purpose of illustrating the invention and do not limit the scope of the invention.

[0094] It should be noted that the "~" sign, which indicates a range of values, includes the values ​​before and after it as the lower and upper limits.

[0095] [Ionic liquid (I)]

[0096] The ionic liquid (I) in the ionic liquid composition for carbon dioxide separation membrane of the present invention is an ionic liquid whose cation is an ammonium having one or more primary or secondary amino groups and an ethylenediamine or propylenediamine skeleton.

[0097] (cation)

[0098] The cation in the ionic liquid (I) of the present invention is an ammonium having a primary amino group bonded to a nitrogen atom with one carbon atom and two hydrogen atoms, or a secondary amino group bonded to a nitrogen atom with two carbon atoms and one hydrogen atom.

[0099] The ammonium has at least one ethylenediamine backbone or propylenediamine backbone. In the case of ammonium having an ethylenediamine backbone, it is represented by the following general formula.

[0100] [Chemical Formula 1]

[0101] Formula 1

[0102] In the formula, R1 and R2 both represent hydrogen atoms, or one represents a hydrogen atom while the other represents a saturated or unsaturated alkyl group that may have substituents. The alkyl group of R1 or R2 is preferably an alkyl group with fewer carbon atoms, such as methyl, ethyl, 2-hydroxyethyl, etc.

[0103] Furthermore, R3, R4, and R5 all represent hydrogen atoms, or two of them represent hydrogen atoms and the other represents a saturated or unsaturated alkyl group that may have substituents, or all of them represent a saturated or unsaturated alkyl group that may have substituents. The alkyl group can be of the same or different types, can be linear or cyclic, can be branched, or can be formed by the bonding of two groups to form a ring.

[0104] Examples of ethylenediamine skeletons represented by Formula 1 above include 2-aminoethylammonium, 2-(N-hydroxyethylamino)ethylammonium, etc.

[0105] [Chemical Formula 2]

[0106]

[0107] Furthermore, the propylenediamine skeleton is a skeleton formed by replacing the ethylene group of the aforementioned ethylenediamine skeleton with a propylene group. Specifically, it is a skeleton formed by replacing the ethylene group of Formula 1 with a propylene group. The carbon atom of the propylene group in the propylenediamine skeleton may have substituents such as alkyl or heteroalkyl groups with a small number of carbon atoms.

[0108] Examples of compounds with a propylenediamine skeleton include 3-aminopropylammonium and 3-(N-methylamino)propylammonium.

[0109] [Chemical Formula 3]

[0110]

[0111] As ammonium in the present invention, it also includes ammonium having two or more ethylenediamine or propylenediamine skeletons. For example, in Formula 1, if either R1 or R2 is aminoethyl, it is diethylenetriammonium; if it is 2-(aminoethyl)aminoethyl, it is triethylenetetraammonium.

[0112] Specifically, examples include 2-(2-(aminoethyl)amino)ethylammonium, 2-(2-(2-(aminoethyl)aminoethyl)amino)ethylammonium, etc.

[0113] [Chemical Formula 4]

[0114]

[0115] (Anions)

[0116] The anions in the ionic liquid (I) are not particularly limited, but amides such as bis(trifluoromethanesulfonyl)amide and dicyandiamide are preferred; sulfonates such as methanesulfonates and trifluoromethanesulfonates; sulfates such as methyl sulfate and ethyl sulfate; halide ions such as fluoride ions, chloride ions, bromide ions, and iodide ions; carboxylates such as trifluoroacetate, etc., and amide-based anions such as bis(trifluoromethanesulfonyl)amide (abbreviated as [Tf2N]) are particularly preferred.

[0117] As preferred ionic liquids (I), the following ionic liquids can be listed, among which [HDAH] [Tf2N] is preferred.

[0118] [Chemical Formula 5]

[0119]

[0120] [Ionic Liquid (II)]

[0121] The ionic liquid (II) in the ionic liquid composition for carbon dioxide separation membrane of the present invention is an ionic liquid in which the cation does not have a primary or secondary amino group and the anion is an oxyacid anion.

[0122] (Oxyacid anions)

[0123] Examples of oxyacid anions include carboxylates such as acetate, propionate, butyrate, and lactate; phosphates such as dimethyl phosphate, diethyl phosphate, and dibutyl phosphate; phosphonates such as methylphosphonate, ethylphosphonate, and butylphosphonate; sulfates such as methyl sulfate, ethyl sulfate, and octyl sulfate; and sulfonates such as methanesulfonate and toluenesulfonate. Preferably, the anion is selected from one or more of the carboxylates, phosphates, and phosphonates shown below.

[0124] [Chemical Formula 6]

[0125]

[0126] In the formula, R1 and R2 represent unsubstituted or substituted saturated or unsaturated alkyl groups.

[0127] Particularly preferred are acetate (abbreviated as [AcO]), 2-(1-methoxyethoxy)propionate (abbreviated as [1O2OPrO]), etc., as carboxylate salts, and methylphosphonate (abbreviated as [MeHPO3]), etc., as phosphonates.

[0128] (cation)

[0129] The cation in the ionic liquid (II) of the present invention is not particularly limited as long as it does not have a primary or secondary amino group. Examples include: imidazolium-type 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, etc.; N-butyl-N,N,N,-trimethylammonium, N,N,N,N,-tetrabutylammonium, N-(2-hydroxyethyl)-N,N,N,-trimethylammonium, N,N-diethyl-N-methyl-N Ammonium compounds such as heptylammonium and N,N-diethyl-N-methyl-N-(6-hydroxyhexyl)ammonium; pyridine-onium compounds such as N-methylpyridinium, N-ethylpyridinium, and N-butylpyridinium; pyrrolidine-onium compounds such as N,N-dimethylpyrrolidine-onium, N-methyl-N-ethylpyrrolidine-onium, and N-methyl-N-butylpyrrolidine-onium; phosphonium compounds such as tetrabutylphosphonium, triethyloctylphosphonium, tributyloctylphosphonium, and trihexyltetradecylphosphonium, etc., with particular preference for imidazolium compounds such as 1,3-dialkylimidazolium with alkyl side chains.

[0130] In dialkylimidazolium with alkyl side chains, shortening the alkyl side chain reduces gas solubility due to physical absorption, thereby increasing selectivity for nitrogen and the like (see Comparative Examples 3 and 4 described below). 1-Ethyl-3-methylimidazolium (abbreviated as [emim]) is particularly preferred.

[0131] As representative ionic liquids (II), the following ionic liquids can be listed.

[0132] [Chemical Formula 7]

[0133]

[0134] [Ratio of the two ionic liquids]

[0135] The preferred mixing ratio of the two ionic liquids for improving the selectivity of carbon dioxide permeation varies depending on the combination of the two ionic liquids.

[0136] For example, when the ionic liquid (I) is [HDAH] [Tf2N] and the ionic liquid (II) is [emim] [AcO], the ionic liquid (I) can improve the permeability selectivity in the range of 5 mol% to 40 mol% relative to the total of the two ionic liquids.

[0137] Furthermore, when the ionic liquid (I) is [HDAH][Tf2N] and the ionic liquid (II) is [emim][MeHPO3], the ionic liquid (I) can improve the permeability selectivity in the range of 5 mol% to 80 mol% relative to the total of the two ionic liquids.

[0138] [Carbon dioxide separation membrane]

[0139] The carbon dioxide separation membrane of the present invention is not particularly limited as long as it can maintain the ionic liquid composition for carbon dioxide separation of the present invention (hereinafter referred to as "ionic liquid composition"). For example, in the case where the carbon dioxide separation membrane has a porous layer, the ionic liquid composition can be impregnated into the membrane to maintain it in the pores of the porous layer.

[0140] Furthermore, in the case where the carbon dioxide separation membrane has a porous layer containing inorganic material particles, similarly, the ionic liquid composition is impregnated into the membrane to remain in the pores of the porous layer.

[0141] Preferred carbon dioxide separation membranes include ionic liquid affinity porous layers (C) and ionic liquid non-affinity porous layers (B) that hold an ionic liquid composition liquid (A) in the pores.

[0142] The ionic liquid affinity porous layer (C) may contain inorganic materials, such as metal oxide particles with an average particle size of 0.001 µm to 5 µm, on a number basis.

[0143] Furthermore, the average thickness of the ionic liquid affinity porous layer (C) is preferably 0.01 µm to 10 µm.

[0144] The following is an explanation of each layer.

[0145] [Ionic liquid non-affinity porous layer (B)]

[0146] The ionic liquid non-affinity porous layer (B) has multiple pores (micropores or voids) internally, and its surface (which may include the surface (or wall) of the internal voids) is generally hydrophobic (relatively hydrophobic compared to the ionic liquid affinity porous layer (C)). Furthermore, the voids may or may not contain individual pores, but at least include interconnecting pores (or through pores) communicating in the thickness direction. The ionic liquid non-affinity porous layer (B) (the material constituting the ionic liquid non-affinity porous layer (B), or the forming component of the ionic liquid non-affinity porous layer (B)) may contain a resin (e.g., a thermoplastic resin) as a main component [e.g., 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more (substantially 100% by weight) relative to the total ionic liquid non-affinity porous layer (B)]. Considering its superior formability and other aspects, ionic liquid non-affinity porous layers (B) are usually porous membranes (porous membranes, porous films or microporous membranes) formed from thermoplastic resins.

[0147] Examples of thermoplastic resins include: polyolefin resins, polyester resins (such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and other polyalkylene aromatic ester resins), polycarbonate resins (such as bisphenol A type polycarbonate resin, bisphenol F type polycarbonate resin, bisphenol S type polycarbonate resin, and other bisphenol-type polycarbonate resins), polyamide resins (such as polyamide 6, polyamide 66, and other aliphatic polyamide resins), polysulfone resins (such as polysulfone, polyethersulfone, etc.), fluoropolymers, and cellulose derivatives.

[0148] These thermoplastic resins can be used alone or in combination of two or more.

[0149] Among these thermoplastic resins, polyolefin resins, fluoropolymers, and cellulose derivatives are preferred (especially polyolefin resins and fluoropolymers, which are considered from the viewpoint of easy availability as polyolefin resins), among which polyethylene resins, polypropylene resins and other polyα-C2-3 olefin resins (especially polyethylene resins), PTFE, PVDF and other fluoropolymers (especially PVDF) are preferred.

[0150] These thermoplastic resins may contain conventional additives. Examples of conventional additives include: heat stabilizers, antioxidants, UV absorbers and other stabilizers, preservatives, bactericides, plasticizers, lubricants, colorants, viscosity modifiers, leveling agents, surfactants, antistatic agents, etc. These additives may be used alone or in combination of two or more. The proportion of additives relative to 100 parts by weight of the resin may be, for example, 50 parts by weight or less, preferably 30 parts by weight or less (e.g., 0.01 to 30 parts by weight), and more preferably 10 parts by weight or less (e.g., 0.1 to 10 parts by weight).

[0151] There are no particular limitations on the preparation method of such porous membranes made of thermoplastic resin. They can be prepared by conventional methods, such as using phase separation of resin solution, stretching of resin membrane, or irradiation of resin membrane with high-energy rays such as alpha rays.

[0152] In addition, in order to adjust the wettability (or contact angle) of the ionic liquid composition (A), conventional surface treatments (such as the treatment described in Japanese Patent Application Publication No. 6-9810, i.e., treatment to attach a crosslinked body derived from an alkene unsaturated monomer having fluorinated alkyl groups) can be applied to the ionic liquid non-affinity porous layer (B).

[0153] As an ionic liquid non-affinity porous layer (B), commercially available products can be used, such as "CPORE" manufactured by Ube Maxell Co., Ltd., "UPORE" manufactured by Ube Industries Co., Ltd., and "Durapel" manufactured by Merck Millipore Co., Ltd.

[0154] The average thickness of the ionic liquid non-affinity porous layer (B) can be, for example, 1µm to 200µm, preferably 5µm to 150µm, and more preferably 10µm to 130µm.

[0155] The pore size (average pore size or average micropore diameter) of the ionic liquid non-affinity porous layer (B) can be selected from a wide range, for example, 0.001 µm to 10 µm (e.g., 0.01 µm to 5 µm), and can be, for example, 0.001 µm to 1 µm (e.g., 0.005 µm to 0.5 µm), preferably 0.01 µm to 0.4 µm (e.g., 0.03 µm to 0.35 µm), and more preferably 0.05 µm to 0.3 µm (e.g., 0.07 µm to 0.25 µm). If the pore size is too small, gas permeability may decrease; if it is too large, the ionic liquid composition (A) may permeate and fail to remain in the carbon dioxide separation membrane (the laminate containing the ionic liquid). It should be noted that, within this specification and claims, the pore size (average pore size or average micropore diameter) can be determined by conventional methods such as mercury infiltration.

[0156] The porosity (or porosity) of the ionic liquid non-affinity porous layer (B) can be selected from a wide range of, for example, 1% to 90% (e.g., 10% to 80%), depending on the manufacturing method of the porous layer, and can be, for example, 20% to 85%, preferably 30% to 80%, and more preferably 40% to 75%. If the porosity is too small, gas permeability may decrease; if it is too large, the ionic liquid composition (A) may permeate and fail to remain in the carbon dioxide separation membrane (the laminate containing the ionic liquid). It should be noted that, in this specification and claims, porosity (or porosity) refers to the volume ratio of the voids in the porous layer relative to any entire porous layer (the entire ionic liquid non-affinity porous layer (B) or the entire ionic liquid affinity porous layer (C)), and can be determined by the methods described in the examples described later.

[0157] The interconnected porosity of the ionic liquid non-affinity porous layer (B) can be, for example, 50% or more, preferably 70% or more, and more preferably 90% or more (e.g., substantially 100%). It should be noted that, within this specification and claims, interconnected porosity refers to the volume ratio of interconnected pores to the voids in the porous layer, and can be calculated based on cross-sectional images observed using a scanning electron microscope (SEM) or similar means.

[0158] The contact angle between the ionic liquid non-affinity porous layer (B) and the ionic liquid composition (A) can be, for example, 90° or more (e.g., 90° to 150°), preferably 95° or more (e.g., 95° to 148°), and more preferably 100° or more (e.g., 100° to 145°). If the contact angle is too small, the liquid (A) containing the ionic liquid may permeate and cannot be retained. It should be noted that, within this specification and claims, the contact angle can be determined by the conventional method described above.

[0159] [Ionic liquid affinity porous layer (C) (or second porous layer (C))]

[0160] The ionic liquid affinity porous layer (C) has multiple pores (micropores or voids) internally, and its surface (which may include the surface (or wall) of the internal voids) is typically hydrophilic (relative to the ionic liquid affinity porous layer (B)). Furthermore, the voids may or may not contain individual pores, but at least include interconnecting pores (or through pores) communicating in the thickness direction. The ionic liquid affinity porous layer (C) (the material constituting the ionic liquid affinity porous layer (C) or the composition forming the ionic liquid affinity porous layer (C)) may also include organic materials such as resins as described in the section on the ionic liquid non-affinity porous layer (B) as the main component. However, considering the advantages of excellent formability and mechanical properties, it is preferable to include inorganic materials as the main component in a proportion of, for example, 50% by weight or more, preferably 70% by weight or more, and more preferably 90% by weight or more (substantially 100% by weight) relative to the entire ionic liquid affinity porous layer (C). Therefore, the ionic liquid affinity porous layer (C) can also be an ionic liquid non-affinity porous layer. The porous layer (B) described in the section is formed by hydrophilicating the resin (e.g., hydrophilicated PTFE porous membrane, hydrophilicated PVDF porous membrane, etc.), but it is usually a porous membrane (porous membrane, porous membrane or microporous membrane) formed of inorganic materials. Therefore, when the ionic liquid-affinity porous layer (C) is formed of inorganic materials, it can impart rigidity derived from the inorganic material to the laminate containing the ionic liquid. Thus, even if it is thin, the carbon dioxide separation membrane (the laminate containing the ionic liquid) is easy to handle, effectively improving operability. In particular, it not only effectively suppresses swelling or gelation, which causes a decrease in gas permeability, but also improves dimensional stability, making it preferable.

[0161] As inorganic materials, metal oxides are commonly listed, such as: Group 4A metal oxides (e.g., titanium oxide, zirconium oxide, etc.), Group 5A metal oxides (vanadium oxide, etc.), Group 6A metal oxides (molybdenum oxide, tungsten oxide, etc.), Group 7A metal oxides (manganese oxide, etc.), Group 8 metal oxides (nickel oxide, iron oxide, etc.), Group 1B metal oxides (copper oxide, etc.), Group 2B metal oxides (zinc oxide, etc.), Group 3B metal oxides (aluminum oxide, indium oxide, etc.), Group 4B metal oxides (silicon oxide, tin oxide, etc.), and Group 5B metal oxides (antimony oxide, etc.).

[0162] These metal oxides can be used alone or in combination of two or more. Among these metal oxides, from the viewpoints of affinity (or hydrophilicity) with the ionic liquid composition (A), ease of preparation of dispersions (or slurries) derived from specific gravity, and ease of acquisition, group 3B metal oxides such as alumina and group 4B metal oxides such as silicon oxide (especially group 3B metal oxides such as alumina) are preferred.

[0163] The inorganic material (or metal oxide) may also be in particulate form. The average particle size of the inorganic material (or metal oxide), in terms of the number of particles, may be 0.001 µm to 10 µm (e.g., 0.01 µm to 5 µm), preferably 0.1 µm to 3 µm (e.g., 0.3 µm to 2 µm), and more preferably 0.5 µm to 1.5 µm (e.g., 0.8 µm to 1.2 µm). In this specification and claims, the average particle size may be determined by the methods described in the embodiments described later.

[0164] The shape of the particles is not particularly limited, and can be listed as: spherical (or roughly spherical), ellipsoidal, polyhedral (pyramidal, cubic, cuboid, etc.), plate-like, rod-like, irregular, etc., but irregular shapes are more common. In addition, from the perspective of improving dispersibility, inorganic materials can be surface-treated or untreated.

[0165] If particulate inorganic materials (or metal oxides) are used to prepare the ionic liquid affinity porous layer (C), the gas permeability of the ionic liquid affinity porous layer (C) itself can be adjusted to be high through the gaps (voids) between the particles. Therefore, even when a laminated structure is formed, the reduction in gas permeability can be effectively suppressed. In addition, even when in contact with the surface of a carbon dioxide separation membrane (e.g., the side of the ionic liquid affinity porous layer (C) in the carbon dioxide separation membrane), the rigidity of the ionic liquid affinity porous layer (C) may prevent the encapsulated liquid containing the ionic liquid (A) from easily seeping out. Therefore, the ionic liquid composition (A) can be stably maintained in a liquid state, and the stickiness of the surface of the carbon dioxide separation membrane (the laminate containing the ionic liquid) can be effectively suppressed.

[0166] In addition, in order to adjust the wettability (or contact angle) to the ionic liquid composition (A), conventional surface treatments (e.g., treatments using silane coupling agents, etc.) can be applied to the ionic liquid affinity porous layer (C).

[0167] The average thickness of the ionic liquid-affinity porous layer (C) can be selected from, for example, a range of 0.01 µm to 100 µm (e.g., 0.03 µm to 70 µm), for example, 0.05 µm to 50 µm (e.g., 0.1 µm to 30 µm), preferably 0.5 µm to 20 µm (e.g., 1 µm to 15 µm), and more preferably 1 µm to 10 µm (e.g., 2 µm to 7 µm). If the average thickness is too large, the weight of the carbon dioxide separation membrane (the laminate containing the ionic liquid) may increase.

[0168] The pore size (average pore size or average micropore diameter) of the ionic liquid affinity porous layer (C) can be, for example, 0.001 µm to 10 µm (e.g., 0.01 µm to 5 µm). If the pore size is too small, not only may the amount of ionic liquid composition (A) be reduced, but gas permeability may also decrease. If the ionic liquid affinity porous layer (C) is formed from inorganic materials (e.g., metal oxide particles), it is easy to adjust the gas permeability to be high.

[0169] The porosity (or porosity) of the ionic liquid-affinity porous layer (C) can be selected from a wide range, for example, 1% to 90% (e.g., 10% to 80%), and can be, for example, 5% to 70% (e.g., 10% to 60%), preferably 15% to 50% (e.g., 20% to 45%), and more preferably 25% to 40% (e.g., 30% to 35%). If the porosity is too small, not only may the amount of ionic liquid composition (A) be reduced, but gas permeability may also decrease. If it is too large, the liquid (A) containing the ionic liquid may not be stably maintained.

[0170] The interconnected porosity of the ionic liquid affinity porous layer (C) can be, for example, 50% or more, preferably 70% or more, and even more preferably 90% or more (for example, substantially 100%).

[0171] The contact angle between the ionic liquid affinity porous layer (C) and the ionic liquid composition (A) can be, for example, less than 90° (e.g., more than 0° and less than 90°), preferably less than 85° (e.g., 15° to 85°), and more preferably less than 80° (e.g., 30° to 80°). If the contact angle is too large, it may be difficult to retain the ionic liquid composition (A).

[0172] The difference in contact angle between the ionic liquid non-affinity porous layer (B) and the ionic liquid affinity porous layer (C) with respect to the ionic liquid composition (A) can be, for example, 10° or more (e.g., 15° to 55°), preferably 20° or more (e.g., 25° to 50°), and more preferably 30° or more (e.g., 30° to 45°). If the difference in contact angle is too small, it may be difficult to stably maintain the ionic liquid composition (A). Furthermore, if the difference in contact angle is too large, the ionic liquid composition (A) may not extend into a flat shape (or extend along the surface direction) within the ionic liquid affinity porous layer when the weight per unit area is low.

[0173] [Carbon dioxide separation membrane (a laminate containing ionic liquid) and its manufacturing method]

[0174] The carbon dioxide separation membrane (a laminate containing an ionic liquid) of the present invention may include a process (impregnation process) in which a liquid (or impregnation solution) containing an ionic liquid composition (A) is impregnated into the voids of the ionic liquid-affinity porous layer (C) in a laminate having an ionic liquid non-affinity porous layer (B) and an ionic liquid affinity porous layer (C).

[0175] The impregnation solution may consist solely of the ionic liquid composition (A), or it may be a mixture (solution or dispersion) formed by combining the ionic liquid composition (A) with a solvent (or dispersion medium). From the viewpoint of easily achieving thin film thickness calculations for the ionic liquid composition (A), the impregnation solution is preferably a mixture. It should be noted that, in this specification and claims, "equivalent film thickness" refers to the film thickness when a liquid film with the same area as a carbon dioxide separation membrane (a laminate containing an ionic liquid) is formed using the ionic liquid composition (A) contained in a porous layer.

[0176] As a solvent (or dispersion medium), a solvent with a higher volatility than the ionic liquid composition (A) is preferred. Examples include: water, alcohols (methanol, ethanol, isopropanol, butanol, cyclohexanol, and other lower alcohols), ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexyl ketone, etc.), esters (methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl formate, ethyl formate, etc.), ethers (diethyl ether, dioxane, tetrahydrofuran, etc.), aliphatic hydrocarbons (hexane, etc.), alicyclic hydrocarbons (cyclohexane, etc.), aromatic hydrocarbons (benzene, etc.), halogenated hydrocarbons (dichloromethane, dichloroethane, etc.), cellosols (methyl cellosol, ethyl cellosol, etc.), acetic acid cellosols, and amides (dimethylformamide, dimethylacetamide, etc.). These solvents can be used alone or in combination of two or more. Among these solvents, water, alcohols (such as C2-6 alkanols such as methanol, etc.) and other aqueous solvents (or water-soluble solvents) are typically used. The concentration of the ionic liquid composition (A) in the impregnation solution can be, for example, 0.001 to 100% by weight, preferably 0.01 to 50% by weight (e.g., 0.05 to 30% by weight), and more preferably 0.1 to 10% by weight (e.g., 0.1 to 8% by weight).

[0177] There are no particular limitations on the method of impregnating with the impregnating liquid; for example, it can be a method of pressing the impregnating liquid into the substrate. Specifically, the impregnating liquid can be impregnated by: in a laminate (a laminate without ionic liquid) comprising an ionic liquid-incompatible porous layer (B) and an ionic liquid-compatible porous layer (C), contacting the surface of the laminate on the side of the ionic liquid-compatible porous layer (C) (or the outermost layer of the laminate) with the impregnating liquid, and applying pressure (or suction) to the opposite side (the side of the ionic liquid-incompatible porous layer (B)). By such a method, the carbon dioxide separation membrane (a laminate containing ionic liquid) of the present invention can be easily or efficiently formed.

[0178] Furthermore, when using the aforementioned mixture as the impregnation liquid, a carbon dioxide separation membrane (a laminate containing ionic liquid) can be prepared by evaporating the solvent (or dispersion medium) after the impregnation process. By removing the solvent (or dispersion medium), the equivalent membrane thickness of the liquid (A) containing the ionic liquid can be easily adjusted, and thin-film fabrication is also convenient. There are no particular limitations on the method of evaporating the solvent; it can be achieved by appropriately heating and / or reducing the pressure according to the solvent's boiling point and vapor pressure.

[0179] In the carbon dioxide separation membrane (a laminate containing an ionic liquid) of the present invention, it is preferable that, in terms of the content of the ionic liquid composition (A), it does not contain more than 100 parts by volume of the ionic liquid composition (A) relative to the 100 parts by volume of the ionic liquid affinity porous layer (C). That is, preferably, the carbon dioxide separation membrane (a laminate containing an ionic liquid) does not have a layer containing a second ionic liquid that is adjacent to the ionic liquid affinity porous layer (C) containing (or retaining) the ionic liquid composition (A) and contains ionic liquid composition (A) that has failed to enter the pores. Therefore, from the viewpoint of improving the carbon dioxide permeation rate and processability of the carbon dioxide separation membrane (a laminate containing ionic liquid), the ionic liquid-affinity porous layer (C) can be selected from 100 parts by volume or less, for example, 0.1 to 99 parts by volume (e.g., 1 to 90 parts by volume), relative to 100 parts by volume of internal porosity. It can contain, for example, 3 to 80 parts by volume (e.g., 5 to 70 parts by volume), preferably 10 to 50 parts by volume (e.g., 15 to 45 parts by volume), and more preferably 20 to 40 parts by volume (e.g., 25 to 35 parts by volume) of the ionic liquid composition (A). If the amount of ionic liquid composition (A) is too large, the processability may decrease.

[0180] In the carbon dioxide separation membrane (a laminate containing an ionic liquid) of the present invention, the equivalent membrane thickness of the ionic liquid composition (A) can be, for example, 0.01 µm to 5 µm (e.g., 0.05 to 3 µm), preferably 0.1 µm to 2 µm (e.g., 0.15 µm to 1.5 µm), and more preferably 0.2 µm to 1 µm (e.g., 0.2 µm to 0.7 µm). If the equivalent membrane thickness is too large, the permeation rate may decrease.

[0181] It should be noted that a laminate containing both an ionic liquid non-affinity porous layer (B) and an ionic liquid affinity porous layer (C) (a laminate without ionic liquid) can be prepared, for example, by directly or indirectly laminating (or forming) an ionic liquid affinity porous layer (C) on either surface of the ionic liquid non-affinity porous layer (B). The method for laminating (or forming) the ionic liquid affinity porous layer (C) is not particularly limited and can include, for example, pressing, heat welding, or bonding using adhesives or bonding agents. Furthermore, when the ionic liquid affinity porous layer (C) is formed from inorganic materials, it can be formed using conventional methods, such as sintering powdered inorganic materials. However, considering the ease or efficiency of forming the specified porous layer and improving processability, it can be formed by a method including a coating process: coating a dispersion (or slurry) formed by dispersing particulate (or powdered) inorganic materials in a dispersion medium, followed by drying the coating film.

[0182] Examples of dispersion media include, for instance, the same dispersion media as those exemplified in the section on impregnation liquids. These dispersion media can be used alone or in combination of two or more. Water is typically the most commonly used dispersion media. When using water as the dispersion media, a small amount (e.g., 0.01 to 10 parts by weight, preferably 0.1 to 2 parts by weight, relative to 100 parts by weight of the inorganic material) of alcohols such as isopropanol can be added as needed to improve the coatability of the non-ionic liquid porous layer (B).

[0183] In addition, a small amount (e.g., 0.01 to 10 parts by weight, preferably 0.1 to 2 parts by weight, relative to 100 parts by weight of the inorganic material) of binder (or adhesive) may be added as needed. Examples include carboxymethyl cellulose or its salts (sodium salts, etc.), hydroxyalkyl cellulose (hydroxyethyl cellulose, hydroxypropyl cellulose, etc.), water-soluble resins such as methyl cellulose, and latexes such as styrene-butadiene rubber latex. The binder is not essential, but most can readily prepare thick ionic liquid-affinity porous layers (C).

[0184] The concentration of the inorganic material in the dispersion is, for example, 0.1 to 50% by weight relative to the total dispersion, preferably 1 to 30% by weight, and more preferably 3 to 20% by weight (e.g., 5 to 15% by weight).

[0185] There are no particular limitations on coating methods; commonly used methods include: roller coating, air knife coating, doctor blade coating, bar coating, reverse coating, doctor blade coating, comma coating, dip / extrusion coating, die coating, gravure coating, micro-gravure coating, screen coating, dip coating, spray coating, spin coating, etc. Among these methods, doctor blade coating is the most common. It should be noted that multiple coatings of the dispersion (or coating solution) can also be applied as needed.

[0186] In the coating process, after the dispersion is further cast or coated, the dispersion medium is evaporated to dry the coating film. The drying temperature is usually selected according to the boiling point of the dispersion medium, and can be, for example, 50°C to 150°C, preferably 80°C to 120°C, and more preferably 90°C to 110°C.

[0187] It should be noted that the carbon dioxide separation membrane of the present invention (or a laminate without ionic liquid having an ionic liquid non-affinity porous layer (B) and an ionic liquid affinity porous layer (C)) can be a two-layer structure of the ionic liquid non-affinity porous layer (B) and the ionic liquid affinity porous layer (C), or a multi-layer structure of three or more layers (e.g., a 3-5 layer structure, etc.) further including other layers (or a third layer) such as the support layer. As the third layer, there are no particular limitations as long as gas can permeate; examples include the support layer [e.g., a mesh (or sieve) made of metal (stainless steel, etc.) or resin], an adhesive or bonding agent layer, etc. These third layers can be used alone or in combination of two or more. From the viewpoint of gas permeability, the carbon dioxide separation membrane (a laminate containing ionic liquid) of the present invention is preferably a 2-3 layer structure (especially a two-layer structure). Furthermore, from the viewpoint of effectively maintaining or immobilizing the ionic liquid composition (A), it is preferable that the ionic liquid non-affinity porous layer (B) and the ionic liquid affinity porous layer (C) are formed adjacent to each other.

[0188] The carbon dioxide separation membrane (a laminate containing an ionic liquid) obtained in this way has excellent gas permeability, and therefore can be appropriately used, for example, in the agricultural field, as a carbon dioxide separation membrane (carbon dioxide concentration membrane) for fertilizing plants. The carbon dioxide separation membrane of the present invention is generally used with the ionic liquid-affinity porous layer (C) containing the ionic liquid composition (A) as the gas supply side (supply side or upstream side), and the opposite side (ionic liquid non-affinity porous layer (B) side) as the permeation side (or downstream side).

[0189] It should be noted that the carbon dioxide permeability coefficient, nitrogen permeability coefficient, and carbon dioxide selectivity can be determined by the methods described in the examples below.

[0190] [A carbon dioxide concentration device equipped with a carbon dioxide separation membrane]

[0191] The carbon dioxide concentration apparatus of the present invention includes the aforementioned carbon dioxide separation membrane. The shape of the carbon dioxide separation membrane is not particularly limited; for example, it can be a flat membrane, a spiral formed by winding a flat membrane, a hollow fiber membrane, etc. These shapes can be used individually or in combination of two or more. The carbon dioxide separation membrane is usually formed together with a support member for supporting or fixing the carbon dioxide separation membrane to form a membrane assembly (concentration unit or separation unit). The material and shape of the support member are not particularly limited as long as they do not obstruct gas permeation, and are appropriately selected according to the shape of the carbon dioxide separation membrane. Furthermore, the concentration unit may include one carbon dioxide separation membrane, or it may include two or more carbon dioxide separation membranes.

[0192] In addition to the concentration unit, most carbon dioxide concentration apparatuses of the present invention also include an intake unit for supplying a gaseous component containing carbon dioxide (e.g., atmosphere) to the carbon dioxide separation membrane. The intake unit supplies the carbon dioxide-containing gaseous component to the carbon dioxide separation membrane by creating a pressure difference between the upstream side (or gas supply side) and the downstream side (permeation side) of the concentration unit. The intake unit is not particularly limited as long as it can create the pressure difference and can be located either upstream or downstream of the concentration unit. Specifically, it can be, for example, an air compressor located upstream of the concentration unit, or a pump (e.g., a diaphragm pump) located downstream.

[0193] The carbon dioxide concentration apparatus of the present invention can operate (or function) as long as it includes at least the concentration unit and the intake unit, thus simplifying the device configuration (or design) and facilitating miniaturization. Furthermore, even with a high permeation rate (carbon dioxide permeation velocity) and a low pressure differential, carbon dioxide can be effectively or efficiently concentrated (or enriched). Therefore, even small intake units with low intake capacity can operate smoothly.

[0194] Example

[0195] The present invention will now be described in detail based on embodiments and comparative examples.

[0196] It should be noted that the description focuses on the separation of carbon dioxide with low partial pressure, but the examples represent preferred embodiments of the present invention and are not limited to the separation of carbon dioxide with high partial pressure according to the present invention.

[0197] [Preparation method of carbon dioxide separation membrane]

[0198] Carbon dioxide separation membrane (hereinafter referred to as "CO2 separation membrane") is prepared by the following method.

[0199] After cleaning a hydrophilic PTFE filter (Merck Millipore) using ethanol, acetone, and ultrapure water as the substrate, the filter was dried under reduced pressure at 70°C for 12 hours using a vacuum dryer. A specified amount of ionic liquid was added dropwise, and the filter was heated to 40°C while being evacuated using a vacuum pump for 12 hours to allow the ionic liquid to permeate the filter. Excess ionic liquid was wiped off the filter such that it filled 95% to 100% of the filter's pore volume, thus forming a CO2 separation membrane. The same method was used when using alumina-coated filters (Daicel) and titanium oxide-coated filters (Daicel) as the substrate.

[0200] [Evaluation methods for carbon dioxide separation membranes]

[0201] The CO2 permeation coefficient and N2 permeation coefficient of the CO2 separation membrane are used Figure 1 The device is used to determine this.

[0202] In the diagram, 1 represents a CO2 / N2 standard gas cylinder, 2 represents an N2 gas cylinder, 3 represents an Ar gas cylinder, 4-6 represent mass flow controllers, 7 represents a CO2 separation membrane, 8 represents a separation membrane retainer, 9 represents an oven, 10 and 11 represent thermometers and hygrometers, 12 and 14 represent water traps, 13 represents a condenser, 15 and 16 represent back pressure valves, 17 and 20 represent soap film flow meters, 18 represents a gas chromatograph (TCD-GC), and 19 represents a CO2 concentration meter.

[0203] First, the CO2 separation membrane 7 is clamped between two PTFE filters (Advantec) and placed in the membrane holder 8. After the oven 9 is preheated, a CO2 / N2 mixture (CO2 composition of 0.04 mol%, 0.10 mol%, 0.50 mol%, 1.00 mol%) at atmospheric pressure is supplied to the bypass on the supply side at a specified flow rate, and high-purity argon gas (99.99995 mol% or higher) at atmospheric pressure is supplied to the bypass on the permeate side at a specified flow rate. The gas from the supply side after bypassing the bypass is analyzed using a gas chromatograph (Shimadzu / GC-8A) 18 and a CO2 concentration meter (Vaisala / GMP343) 19, confirming that the CO2 composition of the gas from the supply side meets the target values ​​(0.04 mol%, 0.10 mol%, 0.50 mol%, 1.00 mol%). The gas from the permeate side after bypassing the bypass is analyzed using the same method, confirming that the components in the permeate side gas, except for argon, are below the detection limit. Next, the supply-side gas and permeate-side gas are supplied to the separation membrane holder 8 to begin the gas permeation test. The composition of the permeate-side gas is analyzed at fixed time intervals; a steady state is considered reached when the compositions of CO2 and N2 remain constant for more than one hour. The supply-side gas and permeate-side gas are analyzed using a gas chromatograph 18 and a CO2 concentration meter 19, and the flow rates of the gases are measured using soap membrane flow meters 17 and 20 (Horiba Seisakusho / SF-1U). Based on the CO2 composition, N2 composition, and flow rate, the flow rates (cm²) of CO2 and N2 permeating through the CO2 separation membrane per unit time are determined. 3 / s). These values, multiplied by the membrane thickness (cm), are further divided by the membrane area (cm²). 2 The partial pressure difference (cmHg) between the supply side and the permeation side was used to obtain the CO2 permeation coefficient and the N2 permeation coefficient. In the examples and comparative examples, the unit of permeation coefficient was uniformly expressed in Barrer (cm). 3 ・cm / cm 2 ・s・cmHg×10 10In addition, the CO2 selectivity is the ratio of the CO2 transmission coefficient to the N2 transmission coefficient.

[0204] Synthesis of ionic liquids

[0205] (Synthetic Example 1: Synthesis of 3-aminopropylammonium bis(trifluoromethanesulfonyl)amide ([APAH][Tf2N]))

[0206] A methanol solution of bis(trifluoromethanesulfonyl)imide (manufactured by Kanto Chemical, hereinafter referred to as HTf2N) was slowly added dropwise to a methanol solution of 3-aminopropylamine (manufactured by Aldrich). The methanol was then stirred overnight at room temperature to obtain a methanol solution containing [APAH][Tf2N] as shown in the following formula. The methanol was removed by vacuum distillation, and the solution was then dried under vacuum at 50°C for 30 hours to obtain [APAH][Tf2N].

[0207] [Chemical Formula 8]

[0208]

[0209] (Synthetic Example 2: Synthesis of 3-(N-methylamino)propylammonium bis(trifluoromethanesulfonyl)amide ([MAPAH][Tf2N]))

[0210] Except that 3-(N-methylamino)propylamine (Aldrich-made) was used in the raw materials, the following formula [MAPAH][Tf2N] was obtained in the same manner as in Synthesis Example 1.

[0211] [Chemical Formula 9]

[0212]

[0213] (Synthetic Example 3: Synthesis of 3-(N,N-dimethylamino)propylammonium bis(trifluoromethanesulfonyl)amide ([DMAPAH][Tf2N]))

[0214] Except that 3-(N,N-dimethylamino)propylamine (Aldrich) was used in the raw materials, the following formula [DMAPAH][Tf2N] was obtained in the same manner as in Synthesis Example 1.

[0215] [Chemical Formula 10]

[0216]

[0217] (Synthetic Example 4: Synthesis of 2-(N-hydroxyethylamino)ethylammonium bis(trifluoromethylsulfonyl)amide ([HDAH][Tf2N]))

[0218] Except that 2-(N-hydroxyethylamino)ethylamine (Aldrich-made) was used in the raw materials, the following formula [HDAH][Tf2N] was obtained in the same manner as in Synthesis Example 1.

[0219] [Chemical Formula 11]

[0220]

[0221] (Synthetic Example 5: Synthesis of 2-aminoethylammonium bis(trifluoromethylsulfonyl)amide ([EDAH][Tf2N]))

[0222] Except that 2-aminoethylamine (prepared by Nacalai Tesque) was used in the raw materials, the following formula [EDAH][Tf2N] was obtained in the same manner as in Synthesis Example 1.

[0223] [Chemical Formula 12]

[0224]

[0225] (Synthetic Example 6: Synthesis of 2-(2-(aminoethyl)amino)ethylammonium bis(trifluoromethylsulfonyl)amide ([DETAH][Tf2N]))

[0226] Except that 2-(2-(aminoethyl)amino)ethylamine (TCI-made) was used in the raw materials, the following formula [DETAH][Tf2N] was obtained in the same manner as in Synthesis Example 1.

[0227] [Chemical Formula 13]

[0228]

[0229] (Synthetic Example 7: Synthesis of 2-(2-(2-(aminoethyl)aminoethyl)amino)ethylammonium bis(trifluoromethylsulfonyl)amide ([TETAH][Tf2N]))

[0230] Except that 2-(2-(2-(aminoethyl)aminoethyl)amino)ethylamine (made by Sigma-Aldrich) was used in the raw materials, the following formula [TETAH][Tf2N] was obtained in the same manner as in Synthesis Example 1.

[0231] [Chemical Formula 14]

[0232]

[0233] (Synthetic Example 8: Synthesis of 1-ethyl-3-methylimidazolium 3-(2-methoxyethoxy)propionate ([emim][1O2OPrO]))

[0234] N-ethylimidazole (Sigma-Aldrich), dimethyl carbonate (Sigma-Aldrich), and methanol (Wako Purity) were reacted at 120°C for 1 day to obtain a methanol solution of 1-ethyl-3-methylimidazolium methyl carbonate ([emim][CH3OCO2]). The content of [emim][CH3OCO2] in the methanol solution was determined by NMR (Bruker / Avance400). An equal amount of 3-(2-methoxyethoxy)propionate (Kuang Rong Chemical Industry) was slowly added dropwise to the [emim][CH3OCO2] methanol solution, and the reaction was allowed to proceed at room temperature for 1 day. Unreacted reactants were then removed by vacuum distillation and toluene extraction to obtain crude [emim][1O2OPrO]. This crude [emim][1O2OPrO] was then dried under reduced pressure at 40°C for 1 week to remove volatile components, yielding [emim][1O2OPrO] as shown in the formula below.

[0235] [Chemical Formula 15]

[0236]

[0237] (Synthetic Example 9: N,N-Diethyl-N-methyl-N-heptylammonium acetate ([N 1227 Synthesis of [AcO]

[0238] Iodomethane was added dropwise to an acetonitrile solution of N,N-diethyl-N-heptylamine at 40°C and stirred for 21 hours. The reaction solution was concentrated under reduced pressure, and the concentrate was washed with toluene. The concentrated solution was dried under reduced pressure to obtain N,N-diethyl-N-methyl-N-heptylammonium iodide. This N,N-diethyl-N-methyl-N-heptylammonium iodide was dissolved in methanol, and silver oxide (I) was added in portions. After stirring at approximately 25°C for more than 12 hours, the solution was filtered, and the washings obtained from washing the filter residue with methanol were used to obtain the filtrate. Acetic acid was added dropwise to the filtrate at approximately 20°C, and the mixture was stirred. The liquid was concentrated and dried under reduced pressure to obtain [N] as shown in the following formula. 1227 [AcO]

[0239] [Chemical Formula 16]

[0240]

[0241] (Synthetic Example 10: N,N-Diethyl-N-methyl-N-(6-hydroxyhexyl)ammonium acetate ([N 1226OH Synthesis of [AcO]

[0242] Iodomethane was added dropwise to an acetonitrile solution of N,N-diethyl-N-(6-hydroxyhexyl)amine at 40°C and stirred at approximately 25°C. The reaction solution was concentrated under reduced pressure, and the concentrate was washed with toluene. The concentrated solution was dried under reduced pressure to obtain N,N-diethyl-N-methyl-N-(6-hydroxyhexyl)ammonium iodide. This N,N,N-diethyl-N-methyl-N-(6-hydroxyhexyl)ammonium iodide was dissolved in methanol, and silver oxide (I) was added in portions. After stirring at approximately 25°C for more than 12 hours, the solution was filtered, and the washings obtained by washing the filter residue with methanol were used to obtain the filtrate. Silver oxide (I) was added to the filtrate again, and the mixture was stirred and then filtered. Acetic acid was added dropwise to the filtrate at approximately 20°C, and the mixture was stirred. The liquid was concentrated and dried under reduced pressure to obtain [N] as shown in the following formula. 1226OH [AcO]

[0243] [Chemical Formula 17]

[0244]

[0245] [Ionic liquids other than those mentioned above]

[0246] In addition to the ionic liquids obtained in the above-described synthetic examples 1 to 10, the following commercially available ionic liquids were used.

[0247] (1) 1-Ethyl-3-methylimidazolium dicyandiamide ([emim][DCA], Aldrich) as shown in the following formula.

[0248] [Chemical Formula 18]

[0249]

[0250] (2) 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([emim][Tf2N], manufactured by Iolitec) shown in the following formula.

[0251] [Chemical Formula 19]

[0252]

[0253] (3) 1-Octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([omim][Tf2N], manufactured by Iolitec) shown in the following formula.

[0254] [Chemical Formula 20]

[0255]

[0256] (4) 1-Ethyl-3-methylimidazolium methylphosphonate as shown in the following formula ([emim][MeHPO3], manufactured by Kanto Chemical).

[0257] [Chemical Formula 21]

[0258]

[0259] (5) 1-Ethyl-3-methylimidazolium acetate as shown in the following formula ([emim][AcO], Aldrich).

[0260] [Chemical Formula 22]

[0261]

[0262] [Comparative Examples 1-8]

[0263] A CO2 separation membrane prepared using a mixture of an ionic liquid (I) and a diluent with an anion of [Tf2N] ([emim][Tf2N] or [omim][Tf2N] as described in Patent Document 3) was studied. The ionic liquid (I) has one or more ammonium compounds with a primary or secondary amino group and an ethylenediamine or propylenediamine skeleton.

[0264] (Comparative Example 1)

[0265] Based on the CO2 separation membrane preparation method described above, a CO2 separation membrane was prepared by impregnating a hydrophilic PTFE filter with 1-ethyl-3-methylimidazolium dicyandiamide ([emim][DCA]), as Comparative Example 1.

[0266] Regarding the gas permeability coefficient of Comparative Example 1, four CO2 / N2 mixtures with different CO2 compositions (0.04 mol%, 0.10 mol%, 0.50 mol%, 1.00 mol%) were used. The gas permeability coefficient of Comparative Example 1 was measured at a temperature of 40°C, a supply-side gas flow rate of 100 ml / min, and a permeation-side gas flow rate of 20 ml / min. The dependence of CO2 partial pressure on the permeability coefficient was studied. The obtained CO2 permeability coefficient, N2 permeability coefficient, and CO2 selectivity as a function of CO2 partial pressure are shown below. Figure 2 , Figure 3 as well as Figure 4 .

[0267] (Comparative Example 2)

[0268] Except that the ionic liquid impregnated in the hydrophilic PTFE filter was changed to anionic 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([emim][Tf2N]), a CO2 separation membrane was prepared in the same manner as Comparative Example 1, as Comparative Example 2.

[0269] (Comparative Examples 3-8)

[0270] As the ionic liquid used to impregnate the hydrophilic PTFE filter, as shown in Table 1 below, a liquid prepared by mixing 3-aminopropylammonium bis(trifluoromethanesulfonyl)amide ([APAH][Tf2N]) obtained in Synthesis Example 1, 3-(N-methylamino)propylammonium bis(trifluoromethanesulfonyl)amide ([MAPAH][Tf2N]) obtained in Synthesis Example 2, bis(trifluoromethanesulfonyl)amide ([DMAPAH][Tf2N]) obtained in Synthesis Example 3, or 2-(N-hydroxyethylamino)ethylammonium bis(trifluoromethanesulfonyl)amide ([HDAH][Tf2N]) obtained in Synthesis Example 4 with [emim][Tf2N] or 1-octyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([omim][Tf2N]) was used. Otherwise, CO2 separation membranes were prepared in the same manner as in Comparative Example 1, as Comparative Examples 3 to 8.

[0271] [Table 1]

[0272]

[0273] The gas coefficients of Comparative Examples 2 to 8 were measured under the same conditions as Comparative Example 1, and the dependence of CO2 partial pressure was studied.

[0274] The CO2 partial pressure dependence of the obtained CO2 permeability coefficient, N2 permeability coefficient, and CO2 selectivity is shown in the figure. Figure 5 , Figure 6 as well as Figure 7 .

[0275] In the figure, □: Comparative Example 2, ■: Comparative Example 3, ▲: Comparative Example 4, ◇: Comparative Example 5, ◆: Comparative Example 6, 〇: Comparative Example 7, ●: Comparative Example 8.

[0276] exist Figure 5 , 6 In the middle, the plots of ■ (Comparative Example 3) and ◆ (Comparative Example 6) overlap.

[0277] In addition, Figure 7 In the middle, the markings are overlapping except for ▲ (Comparative Example 4) and 〇 (Comparative Example 7).

[0278] In addition, in order to study the temperature dependence, in Comparative Examples 2 and 5, the temperature was changed to 80°C and the measurements were performed under the same conditions as in Comparative Example 1.

[0279] The temperature dependence of the obtained CO2 permeability coefficient, N2 permeability coefficient, and CO2 selectivity is shown in the figure. Figure 8 , Figure 9 as well as Figure 10 .

[0280] In the diagram, □ represents Comparative Example 2, and ■ represents Comparative Example 5.

[0281] [summary]

[0282] according to Figure 5 and Figure 7 Compared to Comparative Example 2 (□) which used [emim][Tf2N], Comparative Examples 3 (■), 5 (◇), and 6 (◆) showed decreased CO2 permeation coefficients and CO2 selectivity. This indicates that mixing [emim][Tf2N] with [APAH][Tf2N], [MAPAH][Tf2N], or [DMAPAH][Tf2N] is ineffective in improving the CO2 permeation selectivity of the separation membrane.

[0283] In addition, according to Figure 8 and Figure 10 Even when the temperature is increased from 40°C to 80°C, the CO2 permeability selectivity of Comparative Example 5 (■) is still lower than that of Comparative Example 2 (□).

[0284] Moreover, according to Figure 5 and Figure 7 In contrast to Comparative Example 3 (■), Comparative Example 4 (▲) used [omim][Tf2N] obtained by elongating the alkyl chain of the imidazolium cation instead of [emim][Tf2N]. Compared with Comparative Example 3, the CO2 permeability coefficient and CO2 selectivity were further reduced. In addition, the N2 permeability coefficient of Comparative Example 4 was increased compared with Comparative Example 3.

[0285] On the other hand, such as Figure 5 and Figure 7 As shown, the CO2 permeability coefficient and CO2 selectivity of Comparative Example 7 (〇) are higher than those of Comparative Example 2 (□) and Comparative Example 8 (●).

[0286] It should be noted that, according to Figure 2 and Figure 3 Comparative Example 1 using [emim] [DCA] and Figure 5 and Figure 6 Compared to Comparative Examples 2, 3, 4, 5, and 6, the CO2 and N2 transmission coefficients are lower. On the other hand, according to... Figure 4 The CO2 selectivity of Comparative Example 1 was higher than that of Comparative Examples 2-6.

[0287] As described above, it was found that mixing [emim][Tf₂N] with [HDAH][Tf₂N], which has hydroxyl and amino groups in its cation, improved CO₂ permeation selectivity compared to using only the individual ionic liquids. However, the resulting CO₂ permeation selectivity is still insufficient.

[0288] Therefore, it was studied that, instead of [emim][Tf2N], an ionic liquid (hydrogen bond accepting ionic liquid) with an oxyacid anion having a higher solubility in the CO2-absorbing product than [emim][Tf2N] was used as an ionic liquid (II) in the solvent of the chemical absorption liquid.

[0289] [Examples 1-6, Comparative Example 9]

[0290] In Examples 1-6 and Comparative Example 9, 1-ethyl-3-methylimidazolium methylphosphonate ([emim][MeHPO3]), which has an oxyacid anion, was used as the ionic liquid (II).

[0291] (Example 1)

[0292] A liquid (HDAH][Tf2N] 20 mol%) was prepared by mixing the [HDAH][Tf2N] with the [emim][MeHPO3].

[0293] The resulting mixture was impregnated into a hydrophilic PTFE filter in the same manner as described above to prepare a CO2 separation membrane, as Example 1.

[0294] (Examples 2-6, Comparative Example 9)

[0295] Except for changing the composition of [HDAH][Tf2N] in Example 1 as shown in Table 2 below, CO2 separation membranes were prepared in the same manner as in Example 1, as Examples 2-5 and Comparative Example 9. Furthermore, except for changing [HDAH][Tf2N] in Example 1 to [APAH][Tf2N], CO2 separation membranes were prepared in the same manner as in Example 1, as Example 6. It should be noted that Comparative Example 8 (composition 100 mol%) was included in Table 2.

[0296] [Table 2]

[0297]

[0298] Using the CO2 to form four different CO2 / N2 mixed gases, the gas permeability coefficients of Examples 1-6 and Comparative Example 9 were measured at a temperature of 40°C, a supply-side gas flow rate of 100 ml / min, and a permeation-side gas flow rate of 20 ml / min. The composition dependence and CO2 partial pressure dependence were studied.

[0299] The composition dependence of CO2 permeability, N2 permeability, and CO2 selectivity at a CO2 partial pressure of 0.04 kPa (CO2 composition 0.04 mol%) is shown in the figure. Figure 11 , Figure 12 as well as Figure 13 It should be noted that Comparative Example 8 (composition 100 mol%) was included in these figures.

[0300] In the figure, □: Examples 1 to 5, Comparative Example 8, and Comparative Example 9; ■: Example 6 and Comparative Example 9.

[0301] Furthermore, the CO2 partial pressure dependence of CO2 permeability, N2 permeability, and CO2 selectivity is shown in the figure. Figure 14 , Figure 15 as well as Figure 16 It should be noted that Comparative Example 8 (composition 100 mol%) was also included in these figures.

[0302] In the figure, ◆: Example 1, ■: Example 2, ◇: Example 3, Δ: Example 4, ▲: Example 5, 〇: Example 6, □: Comparative Example 8, ●: Comparative Example 9.

[0303] exist Figure 15 In the text, the markings ◆ (Example 1), ◇ (Example 3), and ▲ (Example 5) overlap.

[0304] [summary]

[0305] according to Figure 11 and Figure 13 Compared with CO2 separation membranes using only [HDAH] [Tf2N] and [emim] [MeHPO3] (Examples 1-5) (□), CO2 separation membranes using only [HDAH] [Tf2N] (Comparative Example 8) (□) and CO2 separation membranes using only [emim] [MeHPO3] (Comparative Example 9) (■) showed improved CO2 permeation coefficient while the N2 permeation coefficient remained approximately constant, thereby significantly improving CO2 selectivity.

[0306] In addition, according to Figure 14 and Figure 16 The CO2 separation membranes with a mixing ratio of 20:80 (Example 1) (◆) and 80:20 (Example 5) (▲) showed that as the CO2 partial pressure decreased, the CO2 permeation coefficient and CO2 selectivity increased. Furthermore, under CO2 partial pressure conditions up to 1 kPa, they exhibited higher CO2 permeation coefficients and CO2 selectivity compared to Comparative Example 8 (□) and Comparative Example 9 (●). It should be noted that in Comparative Example 8 and Comparative Example 9, there was no CO2 partial pressure dependence as seen in Examples 2 and 5; the CO2 permeation coefficient, N2 permeation coefficient, and CO2 selectivity remained approximately constant.

[0307] In addition, by Figure 11 and Figure 13 and the above Figure 5 and Figure 7 It can be seen that the CO2 separation membrane composed of [APAH][Tf2N] and [emim][MeHPO3] (Example 6) (■) shows a high CO2 permeation coefficient and CO2 selectivity compared with the CO2 separation membrane using only [emim][Tf2N] (Comparative Example 2) (◆), the CO2 separation membrane composed of [APAH][Tf2N] and [emim][Tf2N] (Comparative Example 3) (■), and the CO2 separation membrane using only [emim][MeHPO3] (Comparative Example 9) (■).

[0308] Such an improvement effect was not observed in the CO2 separation membrane (Comparative Example 3) (■) which was a mixture of [emim][Tf2N] and [APAH][Tf2N], which are ionic liquids with weak hydrogen bond acceptance.

[0309] As described above, it is known that CO2 separation membranes using an ionic liquid composition consisting of a mixture of ammonium with an amino group (whether or not it has a hydroxyl group) and a methylphosphonate anion containing an oxyacid, [emim][MeHPO3], exhibit improved CO2 permeation selectivity compared to CO2 separation membranes using only the individual ionic liquids.

[0310] Therefore, in order to verify whether ionic liquids with other oxyacid anions also achieve the same excellent results, the following were investigated: instead of [emim][MeHPO3], 1-ethyl-3-methylimidazolium acetate ([emim][AcO]) or 1-ethyl-3-methylimidazolium 3-(2-methoxyethoxy)propionate ([emim][1O2OPrO]) were used as ionic liquids (II).

[0311] [Examples 7-11, Comparative Example 10]

[0312] In Examples 7-11 and Comparative Example 10, acetate, which is an oxyacid anion, was used as the ionic liquid (II).

[0313] (Example 7)

[0314] A liquid ([HDAH][Tf2N] 5 mol%) was prepared by using [HDAH][Tf2N] as an ionic liquid (I) and mixing [emim][AcO] as an ionic liquid (II).

[0315] The resulting mixture was impregnated into a hydrophilic PTFE filter in the same manner as described above to prepare a CO2 separation membrane, as Example 7.

[0316] (Examples 8-11, Comparative Example 10)

[0317] Except for the changes in the composition (mol%) of [HDAH] [Tf2N] in Example 7 as shown in Table 3 below, CO2 separation membranes were prepared in the same manner as in Example 7, as Examples 8-11 and Comparative Example 10. It should be noted that Comparative Example 8 (100 mol%) was included in Table 2.

[0318] [Table 3]

[0319]

[0320] The gas permeability coefficients of Examples 7-11 and Comparative Example 10 were measured at a temperature of 40°C, a supply-side gas flow rate of 100 ml / min, and a permeation-side gas flow rate of 20 ml / min. The compositional dependence of CO2 permeability coefficient, N2 permeability coefficient, and CO2 selectivity was investigated.

[0321] The composition dependence of CO2 and N2 permeability at a CO2 partial pressure of 0.04 kPa (CO2 composition 0.04 mol%) is shown in the figure. Figure 17 It should be noted that Comparative Example 8 (composition 100 mol%) was included in the figure.

[0322] In the figure, □: CO2 transmission coefficient of Examples 7-11, Comparative Examples 8 and 10, ■: N2 transmission coefficient of Examples 7-11, Comparative Examples 8 and 10.

[0323] The compositional dependence of CO2 selectivity is shown by using ◇. Figure 18 It should be noted that Comparative Example 8 (composition 100 mol%) (◆) was also included in this figure.

[0324] Furthermore, for Example 8 and Comparative Example 10, the gas permeability coefficients of four CO2 / N2 mixed gases with different CO2 compositions were measured at 40°C, and the CO2 permeability coefficient, N2 permeability coefficient, and CO2 selectivity were studied as CO2 partial pressure dependent.

[0325] It should be noted that, in Comparative Example 10, as described above, the measurements were performed at a supply-side gas flow rate of 100 ml / min and a permeation-side gas flow rate of 20 ml / min, while in Example 8, the measurements were performed at a supply-side gas flow rate of 400 ml / min and a permeation-side gas flow rate of 200 ml / min.

[0326] The CO2 partial pressure dependence of the obtained CO2 permeability coefficient, N2 permeability coefficient, and CO2 selectivity is shown in the figure. Figure 19 , Figure 20 as well as Figure 21 .

[0327] In the figure, ■: Example 8, ◆: Comparative Example 10.

[0328] like Figure 19 As shown, in Example 8, the gas flow rate is increased, thereby... Figure 17 The reason for the increased CO2 permeability coefficient is that, due to the increase in gas flow rate, the partial pressure of CO2 on the permeation side decreases, and the pressure difference of CO2 on the supply side and the permeation side increases. However, in the separation membrane of Comparative Example 10, which has a low CO2 permeability coefficient, the CO2 permeability coefficient does not change even when the permeate gas flow rate is increased.

[0329] [Examples 12 and 13]

[0330] In Examples 12 and 13, the differences in the substrates used were investigated.

[0331] (Example 12)

[0332] Except for impregnating the alumina-coated filter with a mixture of [HDAH][Tf2N] and [emim][AcO] (10 mol% of [HDAH][Tf2N] used in Example 8), a CO2 separation membrane was prepared in the same manner as in Example 8, as Example 12.

[0333] (Example 13)

[0334] In addition to impregnating the mixture into the titanium oxide coated filter, a CO2 separation membrane was prepared in the same manner as in Example 12, as Example 13.

[0335] Using the CO2 to form four different CO2 / N2 mixed gases, the gas permeation coefficients of Examples 12 and 13 were measured at a supply-side gas flow rate of 400 ml / min and a permeation-side gas flow rate of 200 ml / min, and the dependence of CO2 partial pressure was studied.

[0336] The CO2 partial pressure dependence of the obtained CO2 permeability coefficient, N2 permeability coefficient, and CO2 selectivity is shown above. Figure 19 , Figure 20 as well as Figure 21 It should be noted that Example 8 and Comparative Example 10 (100 mol%) were included in these figures.

[0337] In the figure, ■: Example 8, ◇: Example 12, 〇: Example 13, ◆: Comparative Example 10.

[0338] [Example 14]

[0339] Instead of [HDAH][Tf2N] used in Example 8, a liquid ([APAH][Tf2N] 10 mol%) was prepared by using [APAH][Tf2N] and mixing [emim][AcO] therein as an ionic liquid (II).

[0340] The resulting mixture was impregnated into a hydrophilic PTFE filter in the same manner as described above to prepare a CO2 separation membrane, as Example 14.

[0341] The gas permeability coefficient of Example 14 was measured at a temperature of 40°C, a gas flow rate of 400 ml / min on the supply side, and a gas flow rate of 40 ml / min on the permeation side, and the composition dependence was studied.

[0342] The composition dependence of CO2 permeability, N2 permeability, and CO2 selectivity at a CO2 partial pressure of 0.04 kPa (CO2 composition 0.04 mol%) is expressed as Δ. Figure 22 , Figure 23 as well as Figure 24 .

[0343] It should be noted that Example 8 (10 mol% of [HDAH][Tf2N]) and Comparative Example 8 (100 mol% of [HDAH][Tf2N]) are also included in these figures, indicated by □.

[0344] [Example 15, Comparative Example 11]

[0345] In Examples 15 and 11, as shown in Table 4 below, 3-(2-methoxyethoxy)propionate, an oxyacid anion, was used as the ionic liquid (II). It should be noted that Comparative Example 8 is included in this table.

[0346] (Example 15)

[0347] Except for the use of a liquid (10 mol% of [HDAH][Tf2N]) formed by mixing [HDAH][Tf2N] and [emim][1O2OPrO] obtained in the synthesis example 8, a CO2 separation membrane was prepared in the same manner as in Example 14, as Example 15.

[0348] (Comparative Example 11)

[0349] In Example 15, a CO2 separation membrane was prepared in the same manner as in Example 15, except that only [emim][1O2OPrO] was used, as Comparative Example 11.

[0350] [Table 4]

[0351]

[0352] The gas permeability coefficients of Example 15 and Comparative Example 11 were measured at 40°C, and the composition dependence was studied.

[0353] It should be noted that in Example 15, the measurement was performed at a supply-side gas flow rate of 400 ml / min and a permeation-side gas flow rate of 200 ml / min, while in Comparative Example 11, the measurement was performed at a supply-side gas flow rate of 100 ml / min and a permeation-side gas flow rate of 20 ml / min.

[0354] The composition dependence of CO2 and N2 permeability at a CO2 partial pressure of 0.04 kPa (CO2 composition 0.04 mol%) is shown above. Figure 17 .

[0355] In the figure, ◇: CO2 transmission coefficient of Example 15, Comparative Examples 8 and 11, ◆: N2 transmission coefficient of Example 15, Comparative Examples 8 and 11.

[0356] It should be noted that the N2 transmittance coefficient of Example 15 (◆) overlaps with that of Example 8 (■).

[0357] Furthermore, the compositional dependence of the obtained CO2 selectivity is shown above using ◆. Figure 18 .

[0358] [summary]

[0359] according to Figure 17 and Figure 18 It was found that CO2 separation membranes using an ionic liquid composed of a mixture of [HDAH], [Tf2N], and [emim] and [AcO] (Examples 7 to 10) showed higher CO2 permeation coefficients and CO2 selectivity compared to CO2 separation membranes using pure ionic liquids (Comparative Examples 8 and 10).

[0360] Furthermore, a CO2 separation membrane using an ionic liquid composed of a mixture of [HDAH][Tf2N] and [emim][AcO] (Example 11) also showed superior CO2 permeation selectivity compared to a CO2 separation membrane using only [HDAH][Tf2N] (Comparative Example 8).

[0361] according to Figure 19 and Figure 21 It is evident that this significant improvement was observed even when the membrane substrate was changed from a hydrophilic PTFE filter (Example 8) to an alumina-coated filter (Example 12) and a titanium oxide-coated filter (Example 13).

[0362] In addition, according to Figure 22 and Figure 24 , even when [HDAH][Tf2N] in Example 8 (□) is changed to [APAH][Tf2N] (Example 14) (Δ), higher CO2 permeability coefficient and CO2 selectivity than those of the CO2 separation membrane using only [emim][AcO] (Comparative Example 10) (■) are exhibited.

[0363] Furthermore, as described in Figure 17 and Figure 18 , after changing [emim][AcO] of Example 8 (■, ◇) to [emim][1O2OPrO] (Example 15) (◆, ◆), although the CO2 permeation selectivity of Example 15 is reduced compared with that of Example 8, compared with the CO2 separation membrane using only [HDAH][Tf2N] (Comparative Example 8) (◇, ◆), the CO2 separation membrane using only [emim][AcO] (Comparative Example 10) (□, ◇), and the CO2 separation membrane using only [emim][1O2OPrO] (Comparative Example 11) (◆, ◆), the CO2 separation membrane of Example 15 still exhibits a higher CO2 permeability coefficient and higher CO2 selectivity.

[0364] Furthermore, compared with Example 1 (□ in Figure 11 , 13 ), Example 8 (□ in Figure 17 , ◇ in Figure 18 ) and Example 15 (◇ in Figure 17 , ◆ in Figure 18 ) exhibit higher CO2 permeability coefficient / CO2 selectivity. It can thus be seen that, compared with the composition using an ionic liquid having a phosphonate (methyl phosphonate) as an anion, the composition using an ionic liquid having a carboxylate (acetate and 3-(2-methoxyethoxy)propionate) as an anion can provide a CO2 separation membrane with more excellent CO2 permeation selectivity.

[0365] [Examples 16 to 20, Comparative Example 12]

[0366] Using 2-aminoethylammonium bis(trifluoromethylsulfonyl)amide ([EDAH][Tf2N]) obtained in the above Synthesis Example 5, 2-(2-(aminoethyl)amino)ethylammonium bis(trifluoromethylsulfonyl)amide ([DETAH][Tf2N]) obtained in the above Synthesis Example 6, and 2-(2-(2-(aminoethyl)aminoethyl)amino)ethylammonium bis(trifluoromethylsulfonyl)amide ([TETAH][Tf2N]) obtained in the above Synthesis Example 7, the effect of ionic liquids (I) other than [HDAH][Tf2N] and [APAH][Tf2N] was studied.

[0367] (Example 16)

[0368] Liquids were prepared by mixing [EDAH] [Tf2N] and [emim] [AcO] as shown in Table 5 below. It should be noted that Examples 14 and Comparative Example 10 are included in Table 5.

[0369] The resulting mixture was impregnated into a hydrophilic PTFE filter in the same manner as described above to prepare a CO2 separation membrane, as Example 16.

[0370] (Examples 17-20, Comparative Example 12)

[0371] Except for the changes to [EDAH] and [Tf2N] in Example 16 as shown in Table 5 below, CO2 separation membranes were prepared in the same manner as in Example 16, as Examples 17-20 and Comparative Example 12.

[0372] [Table 5]

[0373]

[0374] The gas permeability coefficients of Examples 16-20 and Comparative Example 12 were measured at a temperature of 40°C, a supply-side gas flow rate of 400 ml / min, and a permeation-side gas flow rate of 200 ml / min, and the composition dependence was studied.

[0375] The composition dependence of CO2 permeability, N2 permeability, and CO2 selectivity at a CO2 partial pressure of 0.04 kPa (CO2 composition 0.04 mol%) is shown above. Figure 22 , Figure 23 as well as Figure 24 .

[0376] It should be noted that these figures also include Example 8 (10 mol%) and Comparative Example 8 (100 mol%) using the [HDAH] [Tf2N], and Example 14 (10 mol%) and Comparative Example 10 (0 mol%) using the [APAH] [Tf2N].

[0377] The figure shows □: Example 8, Comparative Example 8, Δ: Example 14, ■: Example 16, Comparative Example 10, ◇: Examples 17-19, ◆: Example 20, Comparative Example 12.

[0378] [summary]

[0379] according to Figure 22 and Figure 24It can be seen that the CO2 separation membranes formed by mixing ionic liquid compositions of [EDAH][Tf2N], [DETAH][Tf2N], or [TETAH][Tf2N] with [emim][AcO] (Examples 16 to 20) show higher CO2 permeation coefficients and CO2 selectivity compared to CO2 separation membranes formed by ionic liquid compositions of [emim][AcO] alone (Comparative Example 10) or CO2 separation membranes formed by ionic liquid compositions of [TETAH][Tf2N] alone (Comparative Example 12). It should be noted that, when comparing examples including Example 8 and Example 14, the CO2 permeability coefficient of [HDAH][Tf2N] (Example 8) is the highest, and decreases in the following order: [DETAH][Tf2N] (Example 18), [TETAH][Tf2N] (Example 20), [APAH][Tf2N] (Example 14), and [EDAH][Tf2N] (Example 16).

[0380] As described above, it has been found that, with respect to the ionic liquid (I) of the present invention, the CO2 permeation selectivity of the CO2 separation membrane is improved by changing the molecular structure of its ammonium.

[0381] [Examples 21-22, Comparative Examples 13 and 14]

[0382] The N,N-diethyl-N-methyl-N-heptylammonium acetate ([N]) obtained in Synthesis Example 9 was used. 1227 [AcO]), or N,N-diethyl-N-methyl-N-(6-hydroxyhexyl)ammonium acetate obtained in said synthetic example 10 ([N 1226OH The effects of [AcO] on cations other than [emim] in ionic liquid (II) were investigated.

[0383] (Examples 21 and 22)

[0384] As shown in Table 6 below, [HDAH] [Tf2N] and [N] were prepared. 1227 [AcO] or [N] 1226OH A liquid composed of [AcO] was used to impregnate a hydrophilic PTFE filter in the same manner as described above to prepare a CO2 separation membrane, as Examples 21 and 22 respectively.

[0385] (Comparative Examples 13 and 14)

[0386] Except for the use of only [N] in Examples 21 or 22 1227 [AcO] or [N] 1226OHExcept for AcO, CO2 separation membranes were prepared in the same manner as in Examples 21 and 22, as Comparative Examples 13 and 14. It should be noted that Comparative Example 8 (100 mol%) was added to Table 6.

[0387] [Table 6]

[0388]

[0389] The gas permeability coefficients of Examples 21 and 22 and Comparative Examples 13 and 14 were measured at a temperature of 40°C, a supply-side gas flow rate of 400 ml / min, and a permeation-side gas flow rate of 20 ml / min to 40 ml / min, and the composition dependence was studied.

[0390] The composition dependence of CO2 permeability, N2 permeability, and CO2 selectivity at a CO2 partial pressure of 0.04 kPa (CO2 composition 0.04 mol%) is shown in the figure. Figure 25 , Figure 26 as well as Figure 27 It should be noted that Comparative Example 8 (100 mol% of [HDAH][Tf2N]) was included in these figures.

[0391] In the figure, □: Example 21, ■: Example 22, ◇: Comparative Example 13, ◆: Comparative Example 14, Δ: Comparative Example 8.

[0392] [summary]

[0393] according to Figure 25 and Figure 27 It can be seen that [N] is mixed in [HDAH] [Tf2N]. 1227 [AcO] or [N] 1226OH A CO2 separation membrane formed by an ionic liquid composition of [AcO] (Example 21 or Example 22) and a membrane formed by only [N] 1227 [AcO] or [N] 1226OH Compared to the CO2 separation membrane formed by the ionic liquid composition of [AcO] (Comparative Example 13 or Comparative Example 14) or the CO2 separation membrane formed by the ionic liquid composition of [HDAH] [Tf2N] alone (Comparative Example 8), it showed a high CO2 permeation coefficient and CO2 selectivity.

[0394] As described above, it was found that in ionic liquids (II) with oxyacid anions, even if the molecular structure of the cation is ammonium, the CO2 permeation selectivity of the CO2 separation membrane is improved.

[0395] [Summarize]

[0396] It has been found that the CO2 separation membrane using a composition of two ionic liquids (I) and (II) exhibits a higher CO2 permeation coefficient and CO2 selectivity compared to the CO2 separation membrane using each pure ionic liquid. Ionic liquid (I) is an ionic liquid with ammonium having a primary amino and / or secondary amino group as a cation. Ionic liquid (II) is a hydrogen-bonding acceptor ionic liquid with excellent CO2 solubility and solubility of CO2 products after CO2 absorption, having cations without primary or secondary amino groups and oxyacid anions such as carboxylates, phosphonates, and phosphonates. When the composition of ionic liquid (I) is preferably in the range of 5 mol% to 80 mol%, and particularly preferably in the range of 5 mol% to 40 mol%, a higher improvement in CO2 permeation selectivity can be confirmed. On the other hand, according to the examples and comparative examples, when using ionic liquids such as [emim] and [Tf2N] that do not have oxyacid anions, the excellent effects of improved carbon dioxide permeation and permeation selectivity as described in this invention cannot be obtained.

[0397] That is, in the ionic liquid composition of the present invention, by using an ammonium-based ionic liquid (I) having an amino group and an ionic liquid (II) having oxyacid anions such as carboxylates, phosphates, and phosphonates with excellent hydrogen bond acceptability, not only can the solubility of carbon dioxide be increased, but the diffusion rate of the carrier that reacts with carbon dioxide can also be improved. As a result, it can be said that the carbon dioxide permeability and permeation selectivity of the carbon dioxide separation membrane can be significantly improved.

[0398] Industrial availability

[0399] According to the present invention, carbon dioxide with a partial pressure ranging from high to below 1 kPa can be efficiently separated and recovered. Therefore, it goes without saying that this process can be used to separate and recover high-partial-pressure carbon dioxide emitted from biogas production equipment, biomass power generation equipment, incinerators, chemical plants, steel mills, power plants, etc. For example, it can also be used for high-speed and high-energy-efficiency separation and recovery of low-partial-pressure carbon dioxide (below 1 kPa) contained in air in environments where ventilation is typically difficult, such as the atmosphere, high-rise buildings, and enclosed work spaces. As a result, unused carbon dioxide can be effectively utilized for purposes such as promoting the growth of plants and algae. Furthermore, carbon dioxide can be removed from the space without ventilation, eliminating the need to waste the space's heat energy, thus reducing the energy required for air conditioning.

[0400] Explanation of reference numerals in the attached figures

[0401] 1: Standard CO2 / N2 gas cylinders;

[0402] 2: N2 gas cylinder;

[0403] 3: Ar gas cylinder;

[0404] 4-6: Mass flow controller;

[0405] 7: CO2 separation membrane;

[0406] 8: Separation membrane retainer;

[0407] 9: Drying oven;

[0408] 10, 11: Thermometer and hygrometer;

[0409] 12, 14: Water filter valve;

[0410] 13: Condenser;

[0411] 15, 16: Back pressure valve;

[0412] 17, 20: Soap film flow meter;

[0413] 18: Gas Chromatograph (TCD-GC);

[0414] 19: CO2 concentration meter.

Claims

1. The application of an ionic liquid composition in a carbon dioxide separation membrane. The ionic liquid composition is held within the carbon dioxide separation membrane. The ionic liquid composition contains ionic liquid (I) and ionic liquid (II). The cation of the ionic liquid (I) is one or more ammonium compounds selected from the group consisting of 2-aminoethylammonium, 2-(N-hydroxyethylamino)ethylammonium, 3-aminopropylammonium, 3-(N-methylamino)propylammonium, 3-(N,N-dimethylamino)propylammonium, 2-(2-(aminoethyl)amino)ethylammonium, and 2-(2-(2-(aminoethyl)aminoethyl)amino)ethylammonium). The anion of the ionic liquid (I) is bis(trifluoromethylsulfonyl)amide. The cation of the ionic liquid (II) is selected from one or more of the group consisting of 1-ethyl-3-methylimidazolium, N,N-diethyl-N-methyl-N-heptylammonium and N,N-diethyl-N-methyl-N-(6-hydroxyhexyl)ammonium, and the anion is selected from one or more of the group consisting of acetate, 2-(1-methoxyethoxy)propionate and methylphosphonate.

2. A carbon dioxide separation membrane having a porous layer, wherein an ionic liquid composition for carbon dioxide separation membrane is maintained in the pores of the porous layer. The ionic liquid composition contains ionic liquid (I) and ionic liquid (II). The cation of the ionic liquid (I) is one or more ammonium compounds selected from the group consisting of 2-aminoethylammonium, 2-(N-hydroxyethylamino)ethylammonium, 3-aminopropylammonium, 3-(N-methylamino)propylammonium, 3-(N,N-dimethylamino)propylammonium, 2-(2-(aminoethyl)amino)ethylammonium, and 2-(2-(2-(aminoethyl)aminoethyl)amino)ethylammonium). The anion of the ionic liquid (I) is bis(trifluoromethylsulfonyl)amide. The cation of the ionic liquid (II) is selected from one or more of the group consisting of 1-ethyl-3-methylimidazolium, N,N-diethyl-N-methyl-N-heptylammonium and N,N-diethyl-N-methyl-N-(6-hydroxyhexyl)ammonium, and the anion is selected from one or more of the group consisting of acetate, 2-(1-methoxyethoxy)propionate and methylphosphonate.

3. The carbon dioxide separation membrane according to claim 2, characterized in that, The carbon dioxide separation membrane comprises an ionic liquid affinity porous layer and an ionic liquid non-affinity porous layer, wherein the ionic liquid affinity porous layer retains the ionic liquid composition for the carbon dioxide separation membrane in the pores.

4. The carbon dioxide separation membrane according to claim 3, wherein, The ionic liquid affinity porous layer contains inorganic materials.

5. The carbon dioxide separation membrane according to claim 4, wherein, The inorganic material comprises metal oxide particles with an average particle size of 0.001µm to 5µm based on the number of particles.

6. The carbon dioxide separation membrane according to any one of claims 3 to 5, wherein, The average thickness of the ionic liquid affinity porous layer is 0.01µm to 10µm.

7. The application of the carbon dioxide separation membrane according to any one of claims 2 to 6 in the separation and concentration of carbon dioxide with a partial pressure of less than 1 kPa.

8. A carbon dioxide concentration apparatus, wherein the carbon dioxide concentration apparatus comprises a carbon dioxide separation membrane according to any one of claims 2 to 6.

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